Twisted stem internal finishing tools of helical configuration are used in the finishing of precision products having close tolerance having threaded or drilled holes or other interior curved surfaces. Such tools must therefore provide a uniform and precise finishing face, be durable to withstand continuous rotation and contact with the work piece, and producible in a wide range of sizes with various abrasive grades. Known embodiments of helical internal finishing tools such as disclosed in co-pending application Ser. No. 07/519,632 entitled, Abrasive Finishing Tool, are assembled by arranging and fixing individual bristles or filaments on a tool stem, such as a cotter pin, which is clamped upon the individual abrasive filaments in the bight of the cotter pin and then twisted to form a helical tool. The filaments of such tools may be made from plastic abrasive strips as disclosed in co-pending application Ser. No. 07/471,385 entitled, Abrasive Finishing Elements, Tools Made From Such Elements, and Methods of Making Such Tools.
The difficulty of constructing finishing tools with individual bristles or filaments arises in attempting to arrange and uniformly align each bristle or filament in an exact and precise formation to create the desired tool face dimensions with a precise finishing face to the tool. A tool in which even one of the filament tips is out of alignment from the helical arc formed by the ends of the filaments can damage the work piece by creating a groove or gouge therein. Such tools are also usually too small to be effectively and economically trimmed.
Another problem associated with the production of internal finishing tools having individual bristles or filaments is the difficulty of stacking the bristles to produce a tool with a wide finishing face. Bristles or filaments with a round cross section are particularly difficult to stack. Filaments with a cross section having flat surfaces, though stackable, are difficult to keep aligned or stacked uniformly adjacent one another as they are clamped in the bight of a cotter pin. Misalignment of even a single filament results in an imprecise and unbalanced tool unsuitable for precision applications. It is therefore desirable to have a simplified and low cost method of producing a finishing tool in which the abrasive filaments are arranged in an exact and precise manner, and are easily held in such arrangement when attached to a tool stem.